1. Field of the Invention
This invention relates to respiratory humidifiers and more particularly though not solely to respiratory humidifier conduits used in the breathing circuits of humidifiers to provide humidified gases to a patient or other person in need of such gases.
2. Description of the Prior Art
It is well known that, in an attempt to minimise or eliminate "rain out" or condensation occurring within a respiratory breathing circuit, heating elements have been used to maintain a desired temperature for the gases and the inner conduit walls. The temperature of the gases within the humidifier, when delivered to the patient, is typically 37.degree. C. and, room temperature is typically in the vicinity of 22.degree. C. The heating element has been provided around the outer surface of the conduit so that the heat dissipated by the element is conducted through the conduit wall to heat or maintain the temperature of the gases flowing within the conduit. Respiratory humidifier conduits including heating elements enable the gas delivered by the conduit to be liquid free and of high relative humidity.
Originally, in order to overcome the problem of condensation within the conduit, "water traps" comprising special dishes connected at the mid point of the conduit were used to collect any liquid which may have condensed within the conduit. It is obvious that the use of such a device depends on gravity causing the liquid to flow to the water trap rather than to the patient.
Recently, respiratory conduits have included heater wires external of or even within the conduit. There are major disadvantages associated with providing a heater wire within the conduit. These disadvantages include the additional resistance to the gas flow, impairing the capability of the ventilator which controls the pressure and volume of gases delivered to the patient and cleaning is greatly impaired. When the gases flowing in the conduit are combustible gases such as some gases used in anaesthesia, there is a potential for a fault in the heating element causing sparking which could ignite the gases.
An example of a respiratory humidifier conduit having a heating wire disposed within the conduit is disclosed in Bain U.S. Pat. No. 3,856,051. For the foregoing reasons this arrangement is undesirable.
An example of a respiratory humidifier conduit having heating wires attached external to the conduit is disclosed in German Patent Application No DE 42 44 493. The respiratory humidifier conduit disclosed consists of a cylindrical conduit having spirally wound thereon a rib or ridge which structurally supports the conduit walls acting to prevent kinking of the tube. Heating conductors are positioned either along the ribs or ridges on the outside of the tube or within the ribs or ridges (if the ribs or ridges are tubes wound around the conduit). The respiratory humidifier conduit has the disadvantage that the heating conductors at the base of the ribs or ridges dissipate much of their energy to ambient air. Also, due to its construction, the respiratory conduit disclosed is not supple or easily bent and therefore ill suited to use in conditions which require the conduit to be manipulated to a different shape depending on the individual circumstances of the person requiring the humidified gases. In addition the conduit disclosed is very heavy.
It is, therefore, an object of the present invention to provide a respiratory humidifier conduit which goes some way towards overcoming the above disadvantages or which will at least provide the public with a useful choice.